Cathode-ray tube



350-276, XR- 2612612. SR

eb 1952 c. s. SZEGHO ET AL 2,612,612

CATHODE-RAY TUBE Filed June 25, 1950 CONSTANTIN S. SZEGHOV MARK E. AMDURSKY WILLIAM O. REED INVENTORS BY AW THEIR ATTORNE Patented Sept. 30, 1952 UNITED STATES PATENT OFFICE ATHOB Y rues Constantin S. S zegho, Mark E. Amdursky, and William 0. ReedQChicago, Ill., assignors to The Itauland Corporation, a corporation of Illinois Application June 23, 1950, Serial No. 169,997

3 Claims. 1 hi invention relates to iniase-re re iie s devi es nd more par icul t s eh d i es r the y e wh ch com rise a fluor s ent e ee s herted adja ent. a. la s iewin l te s i ea or eay pic u e. bes an the like.

Qonventional cathode-ray picture tubes used while. his schem ha mat al ea i ed he amqunt i sp eu a r fleetieh, t. has. been felled that such a. plas ic. seating, s no su ieierrt y missed an durable to warr t it use. an a comrnereia basis It is also it that gl re tem a glass artic e caus d hy're leet eri oi e erna light may e redu ed y pro iding he ur a er th art le wit a skeletoniaecl c atin o ub.- s aritia ly sire-q arter wa el ngth i thicknes this expedient s mpractical for applica o a tele p cture tube ee us such a skeletoniae i seati g is eelehs le tiv to r flected gh lvleree er, the s heme lsriewn in t e nrier ar fo reducing glare-have else been f nd t9 r a is such a erluetier in pic ur d fin on as to ma e them. unacceptabl tar gener l. use

It is ntirna y ieet of the present in en i n to previde a new an impr ved maeeer nreduethe de ice in which specular r flec on. xt ia igh s mater ally redu e w theu sub st ntiall-y et ac n tram th pictur selutien- It is a further object of the invention to proide a new and improved eathede-ray Pi t tune of th type c mprising a r s er t sere supp rted a acent a ela s ie ine plate, whic s ecular refieetien ef ex e nal. lisht'irei surfa e e th glass viewl e late is so red ced o b ca ly unnetiee b ei hereb pr vi in an ncreas d 'ee t ast rang ith= eut'ahy substantial sac ifice picture detail- A-a image-re rod c ng e ise ee st et v in as er-dense w h the pres nt inve tion mp ises a fluorescent seree i sup orted atl fa eht a glass iewin plate at. least ne ur ee el h c sear prises a multitude of microscopic ngdularprce tuberances individually of from to "microns n eight and. r te vv m ere is diameter- Such a glass viewing plate is characterized by a eflect i measu ed at an l at l ieri u stantially e ual e he angle f heidehe of a eel m e i'heain of l ht i eeteri at th t al s r a e of he iewihe late at a resale of appro m te 35 grees, e hermal i in he n e fr m 1-5 e e h te e er en ei tha of a mirror suriace,'

T e iea u e oi h re invent on which e beli e t be no el ar e iert w th harti lar in the ppended e a ms- The in nti n, toget er th iurt er e ie nd ad antases thereof, may best he understood he e er by reference to th iellewihs e seript e i ta in e e e wi the a c m an n rawing, he e e a gures Qt whi h ke eierehe a s indi a e ik e ement and n hi h:

Fi ur 1 is a f gmen a s e=e e at r l vi w, pa l n tien o an aeer i d vice constructed in accordance with the invention;

Figure 2 is a an ew re tl e l e or a portion of the glass viewing plate of the device of Figure 1 as seen under arnicroscope;

Figure 3 is a cross-sectional view taken along the line 33 of Figure 2, and

Figure l is a graphical representation useful in und n in th i vehtienv The cathode-ray picture tube of Figure 1 comprises a glass envelope lfl having a glass viewing plate 1 l adjacent the inner surface of which is supported a fluorescent screen 12; pref erably, fluorescent screen I? is affixed to the inner surface of viewing plate ll. An electron u (ne wn er ot er su e me n is provided for exciting fluorescent screen I2 in accordance with a received signal in order to rep uc the mage re resen e t e A eeriductive coating I3 may be provided onthe inner side alls h eh e eh 10 to serve a a fi anode, for the beam-projecting system, and a suitable contact terminal (not shown) may be provided .to permit connection of conductive coating I3 in an external circuit.

The image-reproducing device, of Figure l is entirely conventional in' all respects with the p i n o e eeh te f ass vie i plate II. In accordance with the invention, at least the outer surface of glass viewing; plate H is P ed with a mul itu e ei riiei'eseepi nodular protuberances, in order to reduce the reflectivity of the viewing plate. The appear- .arie ethe ake e e t a iaee l te ehs etee in accordance with the invention is smooth and somewhat cloudy, but not so cloudy as to be opaque. However, when viewed under a highpowered microscope, a rather uniform distribution of minute convex or nodular hills or protuberances may be discerned, as shown in Figures 2 and 3.

Thus, the outer surface of viewing plate H is relieved, or placed in relief, in accordance with the representation of Figure 2, and specular reflection of light from external sources is materially reduced, in comparison With that which would be obtained with a polished surface, by scattering and diffuse reflection. Generally, the greater the height of the individual protuberanoes and the smaller the diameter, the greater the reduction in reflectivity. However, as the reflectivity is reduced with a consequent increase in the scattering of transmitted light, the resolving power of the face plate with respect to a light originating at fluorescent screen 12 is also reduced, and if the process is carried too far, the resulting loss in picture definition can be excessive.

In accordance with the present invention, it has been found that if the microscopic nodular protuberances on the outer surface of glass face plate I l are individually within the range from to microns in height and from to 100 microns in diameter, the sacrifice in picture definition is so slight as to be negligible for all practical purposes. Such a face plate is able to resolve at least 2.2 lines per millimeter, which is approximately 4.5 television scanning lines per millimeter and is quite acceptable in accordance with present television practice.

At the same time, however, the reflectivity with respect to light from external sources is materially reduced. As measured with respect to a collimated beam of light directed at the external surface of the viewing plate at an angle ofapproximately degrees from normal incidence, the reflectivity (measured at an angle of reflection equal to the angle of incidence) of a cathode-ray tube viewing plate constructed in accordance with the invention has been found to lie Within the range from 2 per cent to 4 per cent of that of a mirror surface or perfect reflector, as compared to a figure of substantially '7 per cent for a tube having a polished neutral-tinted filter face plate of approximately 66% transmission as now commonly used or about 9 per cent for a tube having a clear window glass face plate. Moreover, it has been found that the picture definition is correlated with the reflectivity so that all face plates which exhibit diifuse reflection and have a reflectivity (measured in the described manner) within the specified range are acceptable as regards picture detail, while those lying outside the specified range are characterized either by too great a loss of picture detail or by an insufficient reduction in reflectivity.

The desired surface condition may be achieved in accordance with any of a number of processes. For example, the outer surface of the viewing plate may be roughened by liquid honing or vapor blasting, after which the outer surface is subjected to the chemical action of hydrofluoric acid until a reflectivity within the specified range is obtained. This process is specifically disclosed and claimed in the copending application of Constantin S. Szegho et a1., Serial No. 169,998, filed concurrently herewith, for Process for Producing Low-Glare Cathode-Ray Tube Viewing Plates, assigned to the present assignee. Another process which has been successfully employed comprises the steps of frost etching the outer surface, (with a commercial frost etch composition comprising ammonium bifluoride as an active ingredient) to render the surface matte, and subsequently etching with hydrofluoric acid. Still another process which may be employed comprises the steps of fusing a ceramic frit into the outer surface of the viewing plate and subsequently etching with hydrofluoric acid until a reflectivity within the specified range is obtained. Whatever the process used, it has been found that whenever the face plate exhibits diffuse reflection and the reflectivity falls Within the range specified above, the loss of picture definition is so small as to be negligible. When the reflectivity is below the range specified, the loss of picture detail is excessive, while reflectivities above the specified range do not provide a sufficient reduction in glare to warrant the expense of the process.

It has also been found that, for any given value of reflectivity, the picture definition is substantially an inverse linear function of the face plate thickness. This relationship is graphically illustrated in Figure 4, in which the least resolvable separation is plotted as a function of the thickness of the viewing plate, reflectivity being maintained constant. Thus it is apparent that, for a predetermined picture definition, higher reflectivities are required for thicker face plates.

Glass-bulb cathode-ray tubes are characterized by a variation in face plate thickness, the viewing plate having an appreciably greater thickness at the periphery than at the center. Accordingly, in order to obtain acceptable picture definition at the edges of the screen, it is necessary to provide a higher reflectivity than would be necessary if only the center of the screen were to be considered.

The ranges specified for reflectivity, and for the height and diameter of the individual microscopic nodules appearing on the viewing plate surface, are those which have been found acceptable for use in connection with glass-bulb cathode-ray picture tubes. Lower and more narrow limits may be maintained in the production of metal-cone tubes, since the quality of the glass used in the viewing plate is better and more uniform, and since the viewing plate thickness is generally less and more constant, than in the case of the glass-bulb tubes. Thus, the reflectivity of the viewing plate of a metal-cone tube constructed in accordance with the invention may be maintained within the range from 1.0 per cent to 2 per cent of that of a mirror surface, thereby permitting greater uniformity in production and a greater reduction in glare. In order to obtain reflectivity readings within this latter range, it has been found that the microscopic nodular protuberances on the surface must be from 5 to 20 microns in height and from 5 to 25 microns in diameter.

Thus, the present invention provides a new and improved image-reproducing device, and more particularly a novel cathode-ray picture tube, which affords a substantial reduction in glare from external light sources without materially sacrificing picture detail. The correlation between reflectivity and picture definition which has been observed appears to hold without regard for the process with which the viewing plate is treated. This finding facilitates large scale inspection of the treated tubes to determine in advance whether or not the required picture definition may be obtained.

While particular embodiments of the present invention have been shown and described, it is apparent that various changes and modifications may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. An image-reproducing device comprising a fluorescent screen supported adjacent a glass viewing plate at least one surface of which comprises a multitude ofintegral microscopic nodular protuberances individually of from 5 to 20 microns in height and from 5 to 100 microns in diameter.

2. An image-reproducing device comprising a fluorescent screen supported adjacent a glass viewing plate at least one surface of which comprises a multitude of integralmicroscopic nodular protuberances individually of from 5 to 20 microns in height and from 5 to 25 microns in diameter.

3. An image-reproducing device comprising a of which comprises a multitude of integral microscopic nodular protuberances individually of from 6 5 to 20 microns in height and from 5 to microns in diameter. CONSTANTIN s. SZEGHO.

MARK E. AMDURSKY. WILLIAM O. REED.

REFERENCES CITED The following references are of record'in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,176,746 Federico Mar. 28, 1916 1,491,830 Troeger Apr. 29, 1924 1,942,841 Shimizu Jan. 9, 1934 2,090,922 Von Ardenne Aug. 24, 1937 2,091,152 Malpica Aug. 24, 1937 2,169,838 Herbst Aug. 15, 1939 2,197,625 Teves et al Apr. 16, 1940 2,201,245 Ruska et al May 21, 1940 2,222,414 Kudar Nov. 19, 1940 2,289,978 Malter July 14, 1942 2,388,203 Zindel, Jr Oct. 30, 1945 2,419,177 Steadman Apr. 15, 1947 2,473,825 Smith June 21, 1949 2,485,561 Burroughs Oct. 25, 1949 

